Add tasks for all the new languages

Task/Determine-if-only-one-instance-is-running/Nim/determine-if-only-one-instance-is-running.nim

@@ -0,0 +1,19 @@
+import os, posix
+
+let fn = getHomeDir() & "rosetta-code-lock"
+proc ooiUnlink {.noconv.} = discard unlink fn
+
+proc onlyOneInstance =
+  var fl = TFlock(lType: F_WRLCK.cshort, lWhence: SEEK_SET.cshort)
+  var fd = getFileHandle fn.open fmReadWrite
+  if fcntl(fd, F_SETLK, addr fl) < 0:
+    stderr.writeln "Another instance of this program is running"
+    quit 1
+  addQuitProc ooiUnlink
+
+onlyOneInstance()
+
+for i in countdown(10, 1):
+  echo i
+  sleep 1000
+echo "Fin!"